INPUT PARAMETERS

origin_addr
Initial address of buffer (choice).
origin_count
Number of entries in buffer (nonnegative integer).
origin_datatype
Data type of each buffer entry (handle).
target_rank
Rank of target (nonnegative integer).
target_disp
Displacement from start of window to beginning of target
buffer (nonnegative integer).
target_count
Number of entries in target buffer (nonnegative integer).
target_datatype
Data type of each entry in target buffer (handle).
op Reduce operation (handle).
win Window object (handle).
adds the contents of the origin buffer (as defined by origin_addr, ori-gin_count, and origin_datatype) to the buffer specified by the argu-
ments target_count and target_datatype, at offset target_disp, in the
target window specified by target_rank and win, using the operation op.
The target window can only be accessed by processes within the same
node. This is similar to MPI_Put, except that data is combined into the
target area instead of overwriting it.
Any of the predefined operations for MPI_Reduce can be used. User-
defined functions cannot be used. For example, if op is MPI_SUM, each
element of the origin buffer is added to the corresponding element in
the target, replacing the former value in the target.
Each datatype argument must be a predefined data type or a derived data
type, where all basic components are of the same predefined data type.
Both datatype arguments must be constructed from the same predefined
data type. The operation op applies to elements of that predefined
type. The target_datatype argument must not specify overlapping
entries, and the target buffer must fit in the target window.
A new predefined operation, MPI_REPLACE, is defined. It corresponds to
the associative function f(a, b) =b; that is, the current value in the
target memory is replaced by the value supplied by the origin.

FORTRAN 77 NOTES

The MPI standard prescribes portable Fortran syntax for the TARGET_DISP
argument only for Fortran 90. FORTRAN 77 users may use the non-porta-
ble syntax
INTEGER*MPI_ADDRESS_KIND TARGET_DISP
where MPI_ADDRESS_KIND is a constant defined in mpif.h and gives the
length of the declared integer in bytes.

NOTES

MPI_Put is a special case of MPI_Accumulate, with the operation
MPI_REPLACE. Note, however, that MPI_Put and MPI_Accumulate have dif-
ferent constraints on concurrent updates.
It is the user's responsibility to guarantee that, when using the accu-
mulate functions, the target displacement argument is such that
accesses to the window are properly aligned according to the data type
arguments in the call to the MPI_Accumulate function.

ERRORS

Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument. C++ func-
tions do not return errors. If the default error handler is set to
MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
will be used to throw an MPI:Exception object.
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
1.3.4 Nov 11, 2009 MPI_Accumulate(3)